1. Field of the Invention
The present invention relates to a toner and an image forming method using the toner.
2. Description of the Related Art
Recently, there are needs for a toner, which has down-sized particle diameter for achieving high quality output images, has hot offset resistance, has low temperature fixing ability for energy saving, and heat resistant storage stability for enduring the high temperature high humidity environment during storage or transporting after the production thereof. Especially, the electric power consumed during the fixing occupies a large proportion of the electric power consumed in the image formation, and therefore it is very important to improve low temperature fixing ability of the toner.
In the art, a toner produced by a kneading-pulverizing method has been used. A toner produced by the conventional kneading-pulverizing method has irregular shapes with a broad particle size distribution, and it is difficult to obtain smaller particle diameters of a toner by such a method. Therefore, such toner has problems that quality of output images is not sufficiently high, and energy required for fixing is high. In the case a toner contains wax (a releasing agent) for improving a fixing ability, the toner produced by the kneading-pulverizing method has a large amount of the wax present at surfaces of toner particles, as the kneaded product is cracked at the surface of the wax by the pulverization to produce the toner particles. For this reason, the releasing effect is enhanced, but the toner tends to deposit (cause filming) on a carrier, a photoconductor, and a blade. Therefore, such the toner does not have satisfactory characteristics on the whole.
In order to solve the aforementioned problems associated with the kneading-pulverizing method, proposed is a production method of a toner by a polymerization method. The toner produced by this polymerization method can be easily made to have small particle diameters, and has a sharper particle size distribution than that of the toner obtained by the pulverization method, and moreover the releasing agent can be encapsulated in the toner particles. As the toner production method using the polymerization method, disclosed is a method for producing a toner using an elongation reaction product of urethane-modified polyester, as a toner binder, for the purpose of improving low temperature fixing ability and hot offset resistance (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-133665).
Moreover, disclosed is a production method of a toner, which is excellent in both powder flowability and transfer properties with small particle diameters, and is also excellent in heat resistant storage stability, low temperature fixing ability, and hot offset resistance (see, for example, JP-A Nos. 2002-287400 and 2002-351143).
Furthermore, disclosed is a toner production method, which produces a toner binder having stable molecular weight distribution, and has an aging step for achieving both low temperature fixing ability and hot offset resistance of the toner (see for example, Japanese Patent (JP-B) No. 2579150, and JP-A No. 2001-158819).
However, these disclosed techniques do not satisfy a high level of low temperature fixing ability of a toner, which has been recently demanded.
For the purpose of attaining a high level of low temperature fixing ability, disclosed is a toner, which contains a resin including a crystalline polyester resin, and a releasing agent, and which has a see-islands phase separation structure, where the resin and the was are incompatible to each other (see, for example, JP-A No. 2004-46095).
Further, disclosed is a toner containing a crystalline polyester resin, a releasing agent, and a graft polymer (see, for example, JP-A No. 2007-271789).
In accordance with these disclosed techniques, low temperature fixing ability is achieved because a crystalline polyester resin is sharply melted compared to a non-crystalline polyester resin. However, even when the crystalline polyester resin being present as island in the sea-island structure is melted, the non-crystalline polyester resin, which is present as sea that constitutes a large part of the toner particle, is not melted. Unless both the crystalline polyester resin and the non-crystalline polyester resin are melted to a certain degree, the toner cannot be fixed. Accordingly, these disclosed toners do not satisfy a high level of low temperature fixing ability, improvement of which has been further demanded recently. Moreover, in order to further improve low temperature fixing ability of a toner, co-melting of a non-crystalline polyester resin and a crystalline polyester resin can be achieved by a method for lowering glass transition temperature, and a method for reducing a molecular weight. In the case where glass transition temperature and a molecular weight of a non-crystalline polyester resin are simply reduced, a resulting toner has excellent low temperature fixing ability, but it is easily expect that hot offset resistance will occur and heat resistant storage stability of the toner will be degraded because of excessively low melt viscosity of the toner.
Accordingly, there are currently needs for a toner, which has excellent low temperature fixing ability, maintains stable fixing ability in a high temperature region, and has excellent heat resistant storage stability, and a developer containing such toner.